Semiconductor device and fabrication method

ABSTRACT

A semiconductor device comprising a semiconductor substrate having upper and lower surfaces and a hydrogen containing region containing hydrogen and helium is provided. The carrier concentration distribution of the hydrogen containing region has: a first local maximum point; a second local maximum point closest to the first local maximum point among local maximum points positioned between the first local maximum point and the upper surface; a first intermediate point of the local minimum between the first and second local maximum points; and a second intermediate point closest to the second local maximum point among local minimum points or flat points where the carrier concentration remains constant positioned between the second local maximum point and the upper surface. A highest point of a helium concentration peak is positioned between the first and second local maximum points. The carrier concentration is lower at the first intermediate point than the second intermediate point.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/079,545, filed on Oct. 26, 2020, which is a continuation ofInternational Patent Application No. PCT/JP2019/044759, filed on Nov.14, 2019, the entirety of each of which is incorporated herein byreference. The application also claims priority from the followingJapanese patent application, which is explicitly incorporated herein byreference:

No. 2018-215548 filed in JP on Nov. 16, 2018.

BACKGROUND 1. Technical Field

The present invention relates to a semiconductor device and afabrication method.

2. Related Art

Conventionally, it is known to form an N type region by implantinghydrogen to a semiconductor substrate (for example, see Patent document1 and 2).

-   [Patent document 1] Japanese translation of PCT International Patent    Application No. 2017-47285-   [Patent document 2] Japanese translation of PCT International Patent    Application No. 2017-146148

Technical Problem

It is preferred that the shape of a carrier concentration distributioncan be controlled with high accuracy.

General Disclosure

To solve the above-mentioned problem, a first aspect of the presentinvention provides a semiconductor device including a semiconductorsubstrate. The semiconductor substrate may have a hydrogen containingregion that contains hydrogen. The hydrogen containing region maycontain helium in at least some region. A hydrogen chemicalconcentration distribution of the hydrogen containing region in a depthdirection has one or more hydrogen concentration trough portions, and ineach of the hydrogen concentration trough portions the hydrogen chemicalconcentration may be equal to or higher than 1/10 of an oxygen chemicalconcentration.

In each of the hydrogen concentration trough portions, the hydrogenchemical concentration may be equal to or higher than a carbon chemicalconcentration.

The hydrogen chemical concentration distribution of the hydrogencontaining region in the depth direction may have one or more hydrogenconcentration peaks. At the hydrogen concentration peaks, the hydrogenchemical concentration may be equal to or higher than ½ of the oxygenchemical concentration.

In at least one of the hydrogen concentration trough portions, thehydrogen chemical concentration may be equal to or higher than a heliumchemical concentration.

A helium chemical concentration distribution of the hydrogen containingregion in the depth direction may have a helium concentration peak. In ahydrogen concentration trough portion provided at a deeper position thanthe helium concentration peak, the hydrogen chemical concentration maybe equal to or higher than the helium chemical concentration.

The hydrogen chemical concentration distribution may have a plurality ofhydrogen concentration peaks. The full width at half maximum of thehelium concentration peak in the helium chemical concentrationdistribution may be larger than an interval between each of the hydrogenconcentration peaks.

The helium concentration peak may be located between two hydrogenconcentration peaks in the depth direction.

The hydrogen chemical concentration distribution may have two or morehydrogen concentration peaks at deeper positions than the heliumconcentration peak. A carrier concentration distribution of the hydrogencontaining region in the depth direction may have two or more hydrogencorresponding peaks located at substantially the same depth as thehydrogen concentration peak at deeper positions than the heliumconcentration peak. The carrier concentration distribution between eachof the hydrogen corresponding peaks may have no peak at a deeperposition than the helium concentration peak.

The carrier concentration distribution may have a carrier concentrationtrough portion between each of the hydrogen corresponding peaks. A localminimum of the carrier concentration in the carrier concentration troughportion at substantially the same depth position as the heliumconcentration peak may be lower than local minimums of the carrierconcentration in the carrier concentration trough portions before andafter the carrier concentration trough portion. The local minimum of thecarrier concentration in the carrier concentration trough portion atsubstantially the same depth position as the helium concentration peakmay be higher than a base doping concentration in the semiconductorsubstrate.

A second aspect of the present invention provides a fabrication methodof a semiconductor device including a semiconductor substrate. In thefabrication method, a hydrogen containing region may be formed byimplanting hydrogen to the semiconductor substrate. In the fabricationmethod, helium may be implanted to the semiconductor substrate so thatat least some region of the hydrogen containing region contains helium.Hydrogen may be implanted to the semiconductor substrate so that thehydrogen chemical concentration distribution of the hydrogen containingregion in a depth direction has one or more hydrogen concentrationtrough portions, and in at least one hydrogen concentration troughportion the hydrogen chemical concentration is equal to or higher than1/10 of the oxygen chemical concentration.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing one example of a semiconductordevice 100.

FIG. 2 is a diagram showing a reference example of a hydrogen chemicalconcentration distribution, a helium chemical concentration distributionand a carrier concentration distribution along the line A-A in FIG. 1 .

FIG. 3 is a diagram showing a hydrogen chemical concentrationdistribution, a helium chemical concentration distribution and a carrierconcentration distribution according to one example of the presentinvention.

FIG. 4 is a diagram showing another example of a hydrogen chemicalconcentration distribution and a helium chemical concentrationdistribution in a hydrogen containing region 102.

FIG. 5 is a diagram showing one example of the relationship of a heliumchemical concentration distribution and a carrier concentrationdistribution in the hydrogen containing region 102.

FIG. 6 is a view showing an exemplary structure of the semiconductordevice 100.

FIG. 7 is a diagram showing one example of a carrier concentrationdistribution in a depth direction at the position of the line B-B inFIG. 6 .

FIG. 8 is a chart showing some steps in a fabrication method of thesemiconductor device 100.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following describes the present invention through embodiments of theinvention, but the following embodiments do not limit the inventionaccording to the claims. In addition, not all the combinations offeatures described in the embodiment are necessarily required insolutions of the invention.

As used herein, one side in a direction parallel to a depth direction ofa semiconductor substrate is referred to as ‘upper’ and the other sideis referred to as ‘lower’. One surface of two principal surfaces of asubstrate, a layer or other member is referred to as upper surface, andthe other surface is referred to as lower surface. An “upper” and“lower” direction is not limited to a direction of gravity, or adirection in which the semiconductor device is mounted.

In this specification, technical matters may be described usingorthogonal coordinate axes of an X axis, a Y axis, and a Z axis. Theorthogonal coordinate axes are only to specify relative positions ofcomponents, and shall not limit them to specific directions. Forexample, the Z-axis shall not exclusively indicate a height directionrelative to the ground. Further, a +Z axis direction and a −Z axisdirection are directions opposite to each other. When the Z axisdirection is described without describing the sign, it means that thedirection is parallel to the +Z axis and the −Z axis.

In the specification, a case where a term such as “same” or “equal” ismentioned may include an error due to a variation in manufacturing orthe like. The error is, for example, within 10%. Moreover, theexpressions “substantially the same” and “substantially equal” may beused to include the error.

As used herein, a chemical concentration refers to a concentration of animpurity measured regardless of its state of activation. The chemicalconcentration can be measured by, for example, secondary ion massspectrometry (SIMS). In this specification, a doping concentrationrefers to a concentration of donors and acceptors. The concentrationdifference between a donor and an acceptor may be a net dopingconcentration of either the donor or the acceptor whose concentration ishigher than the other. The concentration difference can be measured bythe capacitance-voltage method (CV method). A concentration measured bythe CV method may be used as the carrier concentration. Moreover, thecarrier concentration can also be measured by the spreading resistanceanalysis (SR). In an N type region or a P type region, when the carrierconcentration, the doping concentration or the chemical concentrationhas a peak, the peak value may be the concentration value in the region.In the region, for example, when the carrier concentration, the dopingconcentration or the chemical concentration is approximately uniform,the average value of concentration in the region may be theconcentration value in the region.

When referring merely to a “concentration” herein, it refers to aconcentration per unit volume (/cm³). For example, a chemicalconcentration of an impurity is the number of atoms of the impuritycontained per unit volume (atoms/cm³).

FIG. 1 is a cross sectional view showing one example of a semiconductordevice 100. The semiconductor device 100 is provided with a transistordevice such as an insulated gate bipolar transistor (IGBT) and a diodedevice such as a freewheeling diode (FWD), although structural detailsof these devices are omitted in FIG. 1 .

The semiconductor device 100 includes a semiconductor substrate 10. Thesemiconductor substrate 10 is a substrate that is formed of asemiconductor material. As an example, the semiconductor substrate 10 isa silicon substrate. The semiconductor substrate 10 contains an impuritythat is added intendedly or unintendedly at the time of manufacturing asemiconductor ingot. The semiconductor substrate 10 has a dopingconcentration determined by an impurity or the like implanted at thetime of manufacturing or other substances. The conductivity type of thesemiconductor substrate 10 of the present example is an N− type. In thespecification, the doping concentration in the semiconductor substrate10 may be referred to as base doping concentration Db.

As an example, when the semiconductor ingot is made of silicon, an Ntype impurity (dopant) for setting the base doping concentration Db isphosphorous, antimony, arsenic or the like, and a P type impurity(dopant) is boron, aluminum or the like. The base doping concentrationDb may be lower than the chemical concentration of the dopant of thesemiconductor ingot. As an example, when the dopant is phosphorous orboron, the base doping concentration Db may be equal to or higher than50%, or alternatively equal to or higher than 90%, of the chemicalconcentration of the dopant. As another example, when the dopant isantimony, the base doping concentration Db may be equal to or higherthan 5%, or alternatively equal to or higher than 10%, or alternativelyequal to or higher than 50% of the chemical concentration of the dopant.In addition, the semiconductor substrate 10 may contain carbon andoxygen. The carbon and oxygen may be distributed in the entiresemiconductor substrate 10. A fabrication method of the semiconductoringot is, as an example, the magnetic field application Czochralski(MCZ) method, although other methods may be used. Other methods mayinclude the Czochralski method and the float zone (FZ) method.

The semiconductor substrate 10 has an upper surface 21 and a lowersurface 23. The upper surface 21 and the lower surface 23 are twoprincipal surfaces of the semiconductor substrate 10. In thespecification, orthogonal axes in the plane that is parallel to theupper surface 21 and the lower surface 23 is referred to as an x axisand a y axis, and the perpendicular axis to the upper surface 21 and thelower surface 23 is referred to as a z axis.

The semiconductor substrate 10 has a hydrogen containing region 102 thatcontains hydrogen. In the present example, hydrogen ions are implantedto the hydrogen containing region 102 from the lower surface 23 side ofthe semiconductor substrate 10. In the present example, the hydrogenions are protons. The hydrogen ions may be deuterons or tritons. Thehydrogen containing region 102 is the region where the chemicalconcentration of hydrogen is higher than the chemical concentration ofany of other N type impurities and P type impurities. In the hydrogencontaining region 102, the chemical concentration of hydrogen may beequal to or higher than 100 times the chemical concentration of animpurity, among other N type impurities and P type impurities, whosechemical concentration is the highest. The hydrogen containing region102 may be a region where the chemical concentration of hydrogen isequal to or higher than 10 times the base doping concentration Db. Thehydrogen containing region 102 may be a region where the chemicalconcentration of hydrogen is higher than the base doping concentrationDb. The hydrogen containing region 102 contains helium in at least someregion. The helium may function as an adjustment impurity for adjustingthe lifetime of carriers of the semiconductor substrate 10.

The hydrogen ions implanted from the lower surface 23 of thesemiconductor substrate 10 pass through the interior of thesemiconductor substrate 10 to a depth corresponding to accelerationenergy. In the region where the hydrogen ions have passed through, avacancy defect such as a vacancy (V) or a divacancy (VV) is formed. Inthe specification, unless otherwise specified, a vacancy includes adivacancy. The vacancy defect may contain an unsatisfied valence(dangling bond) that exists in a vacancy or divacancy, and may containan unpaired electron of the dangling bond. Hydrogen is diffused byperforming thermal treatment of the semiconductor substrate 10 afterimplanting hydrogen ions. The diffused hydrogen attaches to a vacancyand oxygen, thereby forming a VOH defect. The VOH defect serves as adonor that provides an electron. In addition, the diffused hydrogenitself is activated to serve as a hydrogen donor. Therefore, thehydrogen containing region 102 becomes an N+ type region where thechemical concentration of hydrogen is higher than the base dopingconcentration Db. Note that, unless otherwise specified in thespecification, the term “VOH defect” is used to include a hydrogen donoror alternatively a donor that is newly formed by hydrogen ionimplantation.

The hydrogen containing region 102 of the present example includes alifetime control region 104. The lifetime control region 104 is a regionwhere the lifetime of carriers is reduced because a lifetime killer thatadjusts the lifetime of carriers is formed in the region. The lifetimekiller is a recombination center of carriers, which may be a crystaldefect, and may be a vacancy defect such as a vacancy and a divacancy, adefect complex thereof with an element constituting the semiconductorsubstrate 10 or impurities other than this element, a disposition, arare gas element such as helium, neon, argon or the like, or a metalelement such as platinum or the like. In the present example, a vacancydefect caused by implanting helium to the semiconductor substrate 10,for example, serves as a lifetime killer.

In the present example, the lifetime control region 104 is formed byimplanting helium from the lower surface 23 side of the semiconductorsubstrate 10. In the specification, when a relative position in thedepth direction of the semiconductor substrate 10 is expressed as forexample deep or shallow, such depth is measured relative to the lowersurface 23. That is, an element that is provided at a deeper position ismore spaced from the lower surface 23, and an element that is providedat a shallower position is less spaced from the lower surface 23. Notethat, when a depth is represented with a reference plane specified, thedepth from said reference plane is indicated.

A drift region 18 may be provided in the semiconductor substrate 10. Thedrift region 18 is a region of N− type having a doping concentrationlower than that of the hydrogen containing region 102. The dopingconcentration of the drift region 18 may be the same as the base dopingconcentration Db. The drift region 18 may include a region where thedoping concentration is higher than the base doping concentration Db. Adoping concentration distribution of the drift region 18 may beapproximately uniform or flat within a predetermined depth range L0. Theuniform or flat distribution means that, as an example, within thepredetermined depth range L0, a variation in the doping concentrationfalls within the value range of no less than 80% and no more than 120%of the base doping concentration Db. The predetermined depth range L0may be a length within 10% (that is, L0≤0.1 W0), or may be a lengthwithin 30% (that is, L0≤0.3 W0), or may be a length within 50% (that is,L0≤0.5 W0), or may be a length within 70% (that is, L0≤0.7 W0) of thethickness W0 of the semiconductor substrate 10.

FIG. 2 is a diagram showing a reference example of a hydrogen chemicalconcentration distribution, a helium chemical concentration distributionand a carrier concentration distribution along the line A-A in FIG. 1 .The line A-A contains the entire hydrogen containing region 102 in thedepth direction and a part of the drift region 18. In diagrams showing aconcentration distribution such as that in FIG. 2 or the like, avertical axis is a logarithmic axis that indicates each concentration,and a horizontal axis is a linear axis that indicates a depth positionfrom the lower surface 23. Note that a concentration distribution ineach drawing shows a distribution upon completion of the semiconductordevice 100 (that is, after thermal treatment). In addition, the hydrogenchemical concentration and the helium chemical concentration in FIG. 2is concentration measured, for example, by SIMS method. The carrierconcentration in FIG. 2 is measured by SR method, for example.

The hydrogen chemical concentration distribution in the hydrogencontaining region 102 has one or more hydrogen concentration peaks 115and one or more hydrogen concentration trough portions 114. If thehydrogen chemical concentration distribution has a plurality of hydrogenconcentration peaks 115, hydrogen ions may be implanted to thesemiconductor substrate 10 multiple times with varied ranges. Variedranges may be varied acceleration energies of hydrogen ions upon ionimplantation. The hydrogen chemical concentration distribution in thepresent example has, in order from the lower surface 23 side of thesemiconductor substrate 10, a hydrogen concentration peak 115-1, ahydrogen concentration trough portion 114-1, a hydrogen concentrationpeak 115-2, a hydrogen concentration trough portion 114-2, a hydrogenconcentration peak 115-3, a hydrogen concentration trough portion 114-3,and a hydrogen concentration peak 115-4. A peak may be a mountain-shapedportion that contains a point of a local maximum in a concentrationdistribution. A trough portion may be a trough-shaped portion thatcontains a point of a local minimum in a concentration distribution.

The helium chemical concentration distribution has a heliumconcentration peak 113. The helium concentration peak 113 may be locatedbetween two hydrogen concentration peaks 115 (in the present example,the hydrogen concentration peak 115-2 and the hydrogen concentrationpeak 115-3). For example, a depth position at which the heliumconcentration peak 113 has its local maximum is not contained within therange of the full width at half maximum (FWHM) of any of the hydrogenconcentration peaks 115. Offsetting the position of the heliumconcentration peak 113 from those of the hydrogen concentration peaks115 can leave vacancy defects formed by helium radiation unattached tohydrogen. As a result, carrier lifetime can be reduced. Thus, thelifetime control region 104 can be easily formed. If helium is implantedfrom the lower surface 23 side, a gradient of the slope closer to thelower surface 23 side than a local maximum of the helium chemicalconcentration distribution tends to be smaller than a gradient of theslope opposite to the lower surface 23.

The carrier concentration distribution has one or more hydrogencorresponding peaks 111. The hydrogen corresponding peaks 111 are peaksin the carrier concentration distribution that are located at the samedepth as the hydrogen concentration peaks 115. Note that the depthpositions of the hydrogen concentration peaks 115 and the depthpositions of the hydrogen corresponding peaks 111 may not be exactlyidentical. For example, if the point where a hydrogen corresponding peak111 has its local maximum is contained within the range of the fullwidth at half maximum of a hydrogen concentration peak 115, the hydrogenconcentration peak 115 and the hydrogen corresponding peak 111 may belocated at the same depth position. The carrier concentrationdistribution in the present example has, in order from the lower surface23 side of the semiconductor substrate 10, a hydrogen corresponding peak111-1, a hydrogen corresponding peak 111-2, a hydrogen correspondingpeak 111-3, and a hydrogen corresponding peak 111-4. A hydrogencorresponding peak 111-m is located at the same depth as a hydrogenconcentration peak 115-m. m is an integer not less than 1.

As described above, in the hydrogen containing region 102, VOH defectsand hydrogen itself serve as donors. Thus, the donor concentrationdistribution and the carrier concentration distribution in the hydrogencontaining region 102 are similar to the hydrogen concentrationdistribution. That is, by controlling the hydrogen concentrationdistribution, the donor concentration distribution and the carrierconcentration distribution in the hydrogen containing region 102 can beadjusted.

When helium is implanted to the lifetime control region 104, vacanciesare formed due to the implantation of helium. Some of the vacanciesbecome VOH defects by attaching to hydrogen and oxygen that exist in thehydrogen containing region 102. In the vicinity of the range of helium,vacancies are formed in high concentration so that at least one ofhydrogen and oxygen is insufficient for the vacancies. Thus, theproportion of vacancies that remains without becoming VOH defectsbecomes higher. As a result, carrier concentration is lowered in thelifetime control region 104. On the other hand, in a region far from therange of helium, the concentration of vacancies is lowered so thathydrogen and oxygen are sufficient for the vacancies. Thus, theproportion of the vacancies that remains without becoming VOH defectsbecomes lower. As a result, in the region far from the range of helium,VOH defects caused by helium implantation may increase the donorconcentration and the carrier concentration. That is, in regions otherthan the lifetime control region 104, the carrier concentrationdistribution may not be similar to the hydrogen concentrationdistribution. This deteriorates controllability of the donorconcentration distribution and the carrier concentration distribution.

The carrier concentration distribution in the present example has ahelium corresponding peak 112 between the hydrogen corresponding peak111-3 and the hydrogen corresponding peak 111-4. The heliumcorresponding peak 112 is the peak of VOH defects caused by heliumimplantation. The helium corresponding peak 112 of the present exampleis located at a deeper position than the helium concentration peak 113.More specifically, at least one hydrogen concentration peak 115 islocated between the helium corresponding peak 112 and the heliumconcentration peak 113.

In the present example, the hydrogen chemical concentration isrelatively high in the region shallower than the helium concentrationpeak 113. Thus, in this region, with the donor concentration caused byhydrogen being sufficiently higher than the donor concentration causedby helium, the carrier concentration distribution and the hydrogenchemical concentration retain their similarity.

Thus, by implanting helium to the hydrogen containing region 102, ahelium corresponding peak 112 or the like may occur in the carrierconcentration distribution and the donor concentration distribution, andthe carrier concentration distribution and the donor concentrationdistribution may not be similar to the hydrogen chemical concentrationdistribution. Therefore, when the lifetime control region 104 is formedin the hydrogen containing region 102 for example, controllability ofthe carrier concentration distribution and the donor concentrationdistribution in the hydrogen containing region 102 is deteriorated.

FIG. 3 is a diagram showing a hydrogen chemical concentrationdistribution, a helium chemical concentration distribution and a carrierconcentration distribution according to one example of the presentinvention. In the semiconductor device 100 of the present example, ahydrogen chemical concentration in a hydrogen containing region 102 ishigher than that of the example described in FIG. 2 . The similarity ofthe carrier concentration distribution and the hydrogen chemicalconcentration distribution and the similarity of the donor concentrationdistribution and the hydrogen chemical concentration distribution can beretained by increasing the hydrogen chemical concentration. This canimprove controllability of the carrier concentration distribution andthe donor concentration distribution. Note that, elements that are notparticularly described in FIG. 3 and subsequent figures may be similarto those of the example in FIG. 2 .

In the present example, a hydrogen chemical concentration in each of thehydrogen concentration trough portions 114 is equal to or higher than1/10 of an oxygen chemical concentration DO. The hydrogen chemicalconcentration in each of the hydrogen concentration trough portions 114has a local minimum of the chemical concentration in the hydrogenconcentration trough portion 114. In FIG. 3 , the oxygen chemicalconcentration DO is uniform in the entire semiconductor substrate 10. Inthe present example, the smallest value D2 of the local minimums of thehydrogen concentration in the plurality of hydrogen concentration troughportions 114 is equal to or higher than 0.1×DO. In FIG. 3 , the hydrogenconcentration trough portion 114-3 has the smallest local minimum D2.

A higher proportion of the oxygen that exists in the hydrogen containingregion 102 can be attached to the vacancies caused by hydrogenimplantation by holding the hydrogen chemical concentration, inparticular, the hydrogen chemical concentration in at least one hydrogenconcentration trough portion 114 equal to or higher than 1/10 of theoxygen chemical concentration DO. That is, this allows a lowerproportion of the oxygen that exists in the hydrogen containing region102 to be attached to the vacancies caused by helium implantation. Thus,controllability of the carrier concentration distribution and the donorconcentration distribution can be improved by increasing the similarityof the carrier concentration distribution and the hydrogen chemicalconcentration distribution and the similarity of the donor concentrationdistribution and the hydrogen chemical concentration distribution.

Helium implantation is preferably performed after steps of hydrogenimplantation and thermal treatment. This enables oxygen to be attachedto the vacancies caused by helium implantation after oxygen is attachedto the vacancies caused by hydrogen implantation. The hydrogen chemicalconcentration in each of the hydrogen concentration trough portions 114may be equal to or higher than 2/10 of the oxygen chemical concentrationDO, or may be equal to or higher than ½ of the oxygen chemicalconcentration DO, or may be equal to or higher than one time the oxygenchemical concentration DO. Alternatively, the hydrogen chemicalconcentration in each of the hydrogen concentration trough portions 114may be higher than the oxygen chemical concentration DO.

In the reference example shown in FIG. 2 , the hydrogen chemicalconcentration D2 in the hydrogen concentration trough portion 114-3 issmaller than 1/10 of the oxygen chemical concentration DO. In this case,the helium corresponding peak 112 occurs in the carrier concentrationdistribution.

In the example shown in FIG. 3 , the carrier concentration distributionbetween each of the hydrogen corresponding peaks 111-3, 111-4 has nohelium corresponding peak 112 at a deeper position than the heliumconcentration peak 113. That is, the carrier concentration distributionbetween the hydrogen corresponding peak 111-3 and the hydrogencorresponding peak 111-4 has no local maximum. The carrier concentrationdistribution between the hydrogen corresponding peak 111-3 and thehydrogen corresponding peak 111-4 may have a downward-convex shape.

The oxygen chemical concentration DO in the hydrogen containing region102 may be no less than 1×10¹⁷/cm³. The oxygen chemical concentration DOin the hydrogen containing region 102 may be no less than 5×10¹⁷/cm³ ormay be no less than 1×10¹⁸/cm³. On the other hand, in order to preventdefects caused by oxygen, the oxygen chemical concentration DO in thehydrogen containing region 102 may be no more than 3×10¹⁸/cm³. Althoughthe helium corresponding peak 112 shown in FIG. 2 becomes more prominentwith a higher oxygen chemical concentration DO, the helium correspondingpeak 112 can be suppressed by holding the hydrogen chemicalconcentration equal to or higher than 1/10 of the oxygen chemicalconcentration DO.

In addition, an experiment showed that, the higher the chemicalconcentration of carbon in the hydrogen containing region 102 is, themore prominent the helium corresponding peak 112 becomes. Even when thechemical concentration of carbon is high, however, the heliumcorresponding peak 112 can be suppressed by holding the hydrogenchemical concentration equal to or higher than 1/10 of the oxygenchemical concentration DO. The chemical concentration of carbon in thehydrogen containing region 102 may be no less than 1×10¹⁴/cm³, or may beno less than 5×10¹⁴/cm³, or may be no less than 1×10¹⁵/cm³.

An MCZ substrate fabricated by using the MCZ method may have arelatively high oxygen chemical concentration and a relatively highcarbon chemical concentration. Also in this case, the heliumcorresponding peak 112 can be suppressed by holding the hydrogenchemical concentration equal to or higher than 1/10 of the oxygenchemical concentration DO. That is, even when a lifetime control region104 is formed in a hydrogen containing region 102 in the MCZ substrate,a carrier concentration distribution and a donor concentrationdistribution in the hydrogen containing region 102 can be controlledwith high accuracy.

In each of the hydrogen concentration trough portions 114, the hydrogenchemical concentration may be equal to or higher than the carbonchemical concentration DC. The helium corresponding peak 112 can besuppressed by increasing the hydrogen chemical concentration. In each ofthe hydrogen concentration trough portions 114, the hydrogen chemicalconcentration may be equal to or higher than 2 times the carbon chemicalconcentration DC, or may be equal to or higher than 5 times the carbonchemical concentration DC, or may be equal to or higher than 10 timesthe carbon chemical concentration DC.

Moreover, a local maximum of the hydrogen chemical concentration in eachof the hydrogen concentration peaks 115 may be equal to or higher than ½of the oxygen chemical concentration DO. In the present example, thesmallest value D4 of the local maximums of the hydrogen concentration inthe plurality of hydrogen concentration peaks 115 is equal to or higherthan 0.5×DO. In FIG. 3 , the hydrogen concentration peak 115-3 has thesmallest local maximum D4. The helium corresponding peak 112 can besuppressed by increasing the hydrogen chemical concentration. A localmaximum of the hydrogen chemical concentration in each of the hydrogenconcentration peaks 115 may be equal to or higher than DO or may beequal to or higher than 2×DO.

Moreover, in at least one hydrogen concentration trough portion 114, thehydrogen chemical concentration may be equal to or higher than thehelium chemical concentration. In the present example, at the hydrogenconcentration trough portion 114-3 provided at a deeper position thanthe helium concentration peak 113, the hydrogen chemical concentrationD2 is equal to or higher than the helium chemical concentration D1. Thehydrogen chemical concentration D2 may be equal to or higher than 1.5times the helium chemical concentration D1 or may be equal to or higherthan 2 times the helium chemical concentration D1. The heliumcorresponding peak 112 can be suppressed by increasing the hydrogenchemical concentration D2 above the helium chemical concentration D1. Inthe hydrogen containing region 102, the hydrogen chemical concentrationmay be equal to or higher than the helium chemical concentration at adeeper position than the hydrogen concentration trough portion 114-3.

At a position VH3 in the hydrogen concentration trough portion 114-3,the hydrogen chemical concentration may be equal to or higher than ahelium chemical concentration. The position VH3 in the hydrogenconcentration trough portion 114-3 is located deeper than the hydrogencorresponding peak 111-3 (or the hydrogen chemical concentration peak115-3) relative to the lower surface 23. Moreover, the hydrogencorresponding peak 111-3 (or the hydrogen chemical concentration peak115-3) is located deeper than the helium concentration peak 113. At aposition VH1 of the hydrogen concentration trough portion 114-1, thehydrogen chemical concentration may be equal to or higher than a heliumchemical concentration. The position VH1 of the hydrogen concentrationtrough portion 114-1 is located shallower than the hydrogencorresponding peak 111-2 (or the hydrogen chemical concentration peak115-2) relative to the lower surface 23. Moreover, the hydrogencorresponding peak 111-2 (or the hydrogen chemical concentration peak115-2) is located shallower than the helium concentration peak 113.

The carrier concentration in the hydrogen containing region 102 may behigher than the base doping concentration Db in the semiconductorsubstrate 10. However, the carrier concentration in the lifetime controlregion 104 may be higher than the base doping concentration Db or may beequal to or lower than the base doping concentration Db.

FIG. 4 is a diagram showing another example of a hydrogen chemicalconcentration distribution and a helium chemical concentrationdistribution in a hydrogen containing region 102. In the presentexample, the hydrogen chemical concentration is equal to or higher thanthe helium chemical concentration in all the hydrogen concentrationtrough portions 114 of the hydrogen chemical concentration distribution.The hydrogen chemical concentration in all the hydrogen concentrationtrough portions 114 may be equal to or higher than the peak value D3 ofthe helium chemical concentration. Thus, the helium corresponding peak112 can be further suppressed.

A width of an inter-peak region between each of the hydrogenconcentration peaks 115 is labeled as L. In the example of FIG. 4 , thewidth of the inter-peak region between the hydrogen concentration peaks115-1 and 115-2 is labeled as L12, the width of the inter-peak regionbetween the hydrogen concentration peak 115-2 and the hydrogenconcentration peak 115-3 is labeled as L23, and the width of theinter-peak region between the hydrogen concentration peak 115-3 and thehydrogen concentration peak 115-4 is labeled as L34.

The full width at half maximum FWHM of the helium concentration peak 113may be larger than the width L of any inter-peak region. A plurality ofhydrogen concentration peaks 115 may be included in the range of thefull width at half maximum FWHM of the helium concentration peak 113. Inthe example of FIG. 4 , the hydrogen concentration peaks 115-2, 115-3are included in the range of the full width at half maximum FWHM. Thefull width at half maximum FWHM of the helium concentration peak 113 maybe no less than 5 μm or may be no less than 10 μm. In the example ofFIG. 3 , the full width at half maximum FWHM of the helium concentrationpeak 113 may be similar to that in the example of FIG. 4 .

A depth position at which the helium concentration peak 113 has itslocal maximum is labeled as PHe. Depth positions at which the hydrogenconcentration peaks 115-1, 115-2, 115-3, and 115-4 have their localmaximums are labeled as PH1, PH2, PH3, and PH4, respectively. Each depthposition corresponds to the range of helium or hydrogen being implantedto the semiconductor substrate 10.

The respective positions PH1, PH2, PH3, and PH4 of the hydrogenconcentration peaks 115 may be located within the range from the lowersurface 23 of the semiconductor substrate 10 to the depth position of2×PHe. By positioning the hydrogen concentration peaks 115 in arelatively narrow range around the helium concentration peak 113, thehydrogen chemical concentration in the hydrogen concentration troughportions 114 can easily be increased. Thus, the helium correspondingpeak 112 can be suppressed. In the example of FIG. 3 , the positions ofthe hydrogen concentration peaks 115 and the helium concentration peak113 may be similar to those of the example of FIG. 4 .

FIG. 5 is a diagram showing one example of the relationship of a heliumchemical concentration distribution and a carrier concentrationdistribution in the hydrogen containing region 102. FIG. 5 also shows apeak 119 of a vacancy defect concentration distribution. The vacancydefect concentration distribution is a concentration distribution ofvacancy defects caused by helium ion implantation. The configurationdescribed in FIG. 5 may be applied to any of the example shown in FIG. 3and the example shown in FIG. 4 .

The carrier concentration distribution has carrier concentration troughportions 116 between each of the hydrogen corresponding peaks 111. Thecarrier concentration distribution in the present example has, in orderfrom the lower surface 23 side of the semiconductor substrate 10, acarrier concentration trough portion 116-1, a carrier concentrationtrough portion 116-2, and a carrier concentration trough portion 116-3.The carrier concentration trough portions 116 may contain a flat regionin which the carrier concentration remains constant.

A local minimum of the carrier concentration in each of the carrierconcentration trough portions 116 is labeled as D5. The local minimum D5is the smallest value of a carrier concentration within a range betweentwo hydrogen corresponding peaks 111.

A local minimum D5-2 of the carrier concentration in the carrierconcentration trough portion 116-2 at the same depth position as thehelium concentration peak 113 may be lower than any of local minimumsD5-1, D5-3 of the carrier concentration of the carrier concentrationtrough portions 116-1, 116-3 before and after this carrier concentrationtrough portion 116-2. Thus, the lifetime control region 104 can beformed. The local minimum D5-2 of the carrier concentration in thecarrier concentration trough portion 116-2 may be higher than the basedoping concentration Db in the semiconductor substrate 10. The localminimums D5-1, D5-3 of the carrier concentration in the carrierconcentration trough portions 116-1, 116-3 may be higher than the basedoping concentration Db in the semiconductor substrate 10.

The peak 119 of the vacancy defect concentration distribution may belocated in the vicinity of the helium concentration peak 113 of thehelium concentration distribution. In the present example, a peakposition PV of the peak 119 is identical to a peak position PHe of thehelium concentration peak 113. The peak 119 of the vacancy defectconcentration distribution has a narrower distribution width than thedistribution width of the helium concentration peak 113 of the heliumconcentration distribution. The peak 119 of the vacancy defectconcentration distribution may be distributed between the hydrogencorresponding peak 111-2 and the hydrogen corresponding peak 111-3 ofthe carrier concentration. Vacancy defects are formed in the interior ofthe semiconductor substrate 10 by ion implantation of an adjustmentimpurity. Hydrogen that exists around the vacancy defects terminates thedangling bonds of the vacancy defects. This decreases the concentrationof the vacancy defects formed in the interior of the semiconductorsubstrate 10. At the hydrogen corresponding peak 111-2 and the hydrogencorresponding peak 111-3 with high hydrogen chemical concentrations, thevacancy defect concentration is particularly decreased because of thehigh hydrogen chemical concentrations. Thus, the vacancy defectconcentration is distributed only between the hydrogen correspondingpeak 111-2 and the hydrogen corresponding peak 111-3. Gradients of theconcentration slopes on both sides of the peak position PV of thevacancy defect concentration distribution may be larger than gradientsof the concentration slopes on both sides of the peak position PHe ofthe helium concentration distribution.

FIG. 6 is a view showing an exemplary structure of the semiconductordevice 100. The semiconductor device 100 of the present example servesas an insulated gate bipolar transistor (IGBT). The semiconductor device100 of the present example has a semiconductor substrate 10, aninterlayer dielectric film 38, an emitter electrode 52 and a collectorelectrode 54. The interlayer dielectric film 38 is formed to cover atleast part of an upper surface 21 of the semiconductor substrate 10. Theinterlayer dielectric film 38 has a through hole such as a contact holeformed therein. The contact hole exposes the upper surface 21 of thesemiconductor substrate 10. The interlayer dielectric film 38 may bemade of a silicate glass such as a PSG, BPSG or the like, and may be anoxide film, a nitride film or the like.

The emitter electrode 52 is formed on the upper surfaces of thesemiconductor substrate 10 and the interlayer dielectric film 38. Theemitter electrode 52 is also formed in the contact hole, and is incontact with the upper surface 21 of the semiconductor substrate 10exposed by the contact hole.

The collector electrode 54 is formed on a lower surface 23 of thesemiconductor substrate 10. The collector electrode 54 may be in contactwith the entire lower surface 23 of the semiconductor substrate 10. Theemitter electrode 52 and the collector electrode 54 are formed of ametal material such as aluminum.

The semiconductor substrate 10 of the present example is provided withan N− type drift region 18, an N+ type emitter region 12, and a P− typebase region 14, an N+ type accumulation region 16, an N+ type bufferregion 20, and a P+ type collector region 22.

The emitter region 12, which is provided in contact with the uppersurface 21 of the semiconductor substrate 10, is a region which has ahigher donor concentration than that of the drift region 18. The emitterregion 12 contains an N type impurity such as, for example, phosphorous.

The base region 14 is provided between the emitter region 12 and thedrift region 18. The base region 14 contains a P type impurity such asboron, for example.

The accumulation region 16, which is provided between the base region 14and the drift region 18, has one or more donor concentration peaks withhigher donor concentrations than that of the drift region 18. Theaccumulation region 16 may contain an N type impurity such asphosphorous, and may contain hydrogen.

The collector region 22 is provided in contact with the lower surface 23of the semiconductor substrate 10. An acceptor concentration of thecollector region 22 may be higher than an acceptor concentration in thebase region 14. The collector region 22 may contain a P type impuritythat is the same as or different from those contained in the base region14.

The buffer region 20 is provided between the collector region 22 and thedrift region 18, and has one or more donor concentration peaks withhigher donor concentrations than that of the drift region 18. The bufferregion 20 contains an N type impurity such as hydrogen. The bufferregion 20 may serve as a field stop layer to prevent a depletion layerexpanded from the lower surface side of the base region 14 from reachingthe collector region 22.

The hydrogen containing region 102 described in FIG. 1 to FIG. 5 isincluded in the buffer region 20. In the present example, the hydrogencontaining region 102 serves as the buffer region 20 as a whole. Thebuffer region 20 of the present example includes the lifetime controlregion 104 described in FIG. 1 to FIG. 5 .

According to the semiconductor device 100 of the present example, thecarrier concentration distribution and the donor concentrationdistribution in the buffer region 20 can be controlled with highaccuracy. Thus, characteristics of the semiconductor device 100 can becontrolled with high accuracy.

A gate trench portion 40 passes through the emitter region 12, the baseregion 14 and the accumulation region 16 from the upper surface 21 ofthe semiconductor substrate 10 to reach the drift region 18. Theaccumulation region 16 of the present example is located above the lowerend of the gate trench portion 40. The accumulation region 16 may beprovided to cover the entire lower surface of the base region 14. Byproviding the accumulation region 16 with a higher concentration thanthat of the drift region 18 between the drift region 18 and the baseregion 14, a carrier injection-enhancement effect (IE effect) can beincreased to reduce the ON voltage in IGBT.

The gate trench portion 40 has a gate trench, a gate insulating film 42and a gate conductive portion 44 formed in the upper surface side of thesemiconductor substrate 10. The gate insulating film 42 is formed tocover an inner wall of the gate trench. The gate insulating film 42 maybe formed by oxidizing or nitriding a semiconductor on the inner wall ofthe gate trench. The gate insulating film 42 is formed inside the gatetrench, and the gate conductive portion 44 is formed inside the gateinsulating film 42. In other words, the gate insulating film 42insulates the gate conductive portion 44 from the semiconductorsubstrate 10. The gate conductive portion 44 is formed of a conductivematerial such as polysilicon.

The gate conductive portion 44 includes a region opposed to the baseregion 14 across the gate insulating film 42. Although in thiscross-section the gate trench portion 40 is covered by the interlayerdielectric film 38 at the upper surface of the semiconductor substrate10, in another cross section the gate conductive portion 44 is connectedto the gate electrode. When a predetermined gate voltage is applied tothe gate conductive portion 44, a channel is formed by an electroninversion layer in a surface layer of the base region 14 at a boundaryin contact with the gate trench portion 40.

FIG. 7 is a diagram showing one example of a carrier concentrationdistribution in a depth direction at the position of the line B-B inFIG. 6 . In FIG. 7 , the vertical axis is a logarithmic axis indicatingthe carrier concentration, and the horizontal axis is a linear axisindicating the distance from the lower surface 23.

The carrier concentration distribution in the buffer region 20 of thepresent example has a plurality of hydrogen corresponding peaks 111provided at different positions in the depth direction. The carrierconcentration distribution in the buffer region 20 can be controlledwith high accuracy, and thus the expansion of the depletion layer fromthe upper surface 21 side can be suppressed with high accuracy.

Although the accumulation region 16 of the present example has aplurality of peaks 25, the accumulation region 16 may have a single peak25. The peak 25 is a peak of the donor concentration. The peak 25 may beformed by hydrogen implantation. In this case, the accumulation region16 may contain the hydrogen containing region 102.

FIG. 8 is a chart showing some steps in a fabrication method of thesemiconductor device 100. FIG. 8 shows a process of forming the hydrogencontaining region 102. Before and after the process shown in FIG. 8 ,each structure shown in FIG. 6 is formed.

In S702, hydrogen ions are implanted from the lower surface 23 side ofthe semiconductor substrate 10. In S702, hydrogen ions may be implantedmultiple times with varied ranges. Next, in S704, the semiconductorsubstrate 10 is annealed. This generates hydrogen donors and VOH defectsand forms the hydrogen containing region 102.

Next, in S706, helium is implanted from the lower surface 23 side of thesemiconductor substrate 10 so that the helium is contained in at leastsome region of the hydrogen containing region 102. The total dosage ofthe hydrogen ions in S702 may be equal to or higher than 5 times thetotal dosage of helium in S706. The helium corresponding peak 112 can besuppressed by increasing the dosage of hydrogen ions. The total dosageof hydrogen ions may be equal to or higher than 10 times the totaldosage of helium. Moreover, the dosage in each range of the hydrogenions may be equal to or higher than 5 times the total dosage of helium.Note that the dosages and ranges in S702 and S706 are adjusted so thateach concentration distribution described in FIG. 1 to FIG. 7 can beobtained.

Next, in S708, the semiconductor substrate 10 is annealed. The annealingcondition in S708 may be the same as or different from the annealingcondition in S704. In S708, a lifetime control region 104 is formed inthe hydrogen containing region 102 by performing thermal treatment ofthe semiconductor substrate 10.

While the embodiments of the present invention have been described, thetechnical scope of the invention is not limited to the above describedembodiments. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiments. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

EXPLANATION OF REFERENCES

10: semiconductor substrate, 12: emitter region, 14: base region, 16:accumulation region, 18: drift region, 20: buffer region, 21: uppersurface, 22: collector region, 23: lower surface, 25: peak, 38:interlayer dielectric film, 40: gate trench portion, 42: gate insulatingfilm, 44: gate conductive portion, 52: emitter electrode, 54: collectorelectrode, 100: semiconductor device, 102: hydrogen containing region,104: lifetime control region, 111: hydrogen corresponding peak, 112:helium corresponding peak, 113: helium concentration peak, 114: hydrogenconcentration trough portion, 115: hydrogen concentration peak, 116:carrier concentration trough portion, 119: peak

What is claimed is:
 1. A semiconductor device comprising a semiconductorsubstrate, the semiconductor substrate having an upper surface and alower surface, wherein the semiconductor substrate has a hydrogencontaining region that contains hydrogen, the hydrogen containing regioncontains helium, a carrier concentration distribution of the hydrogencontaining region in a depth direction has: a first local maximum pointhaving a local maximum value in a carrier concentration; a second localmaximum point positioned closest to the first local maximum point amongone or more upper-side local maximum points positioned between the firstlocal maximum point and the upper surface and each having a localmaximum value in the carrier concentration; a first intermediate pointpositioned between the first local maximum point and the second localmaximum point and having a local minimum value in the carrierconcentration; and a second intermediate point positioned closest to thesecond local maximum point among (i) one or more upper-side localminimum points positioned between the second local maximum point and theupper surface and each having a local minimum value in the carrierconcentration or (ii) a plurality of upper-side flat points at which thecarrier concentration remains constant in the depth direction, theplurality of upper-side flat points positioned between the second localmaximum point and the upper surface, a highest point of a heliumconcentration peak in a helium chemical concentration distribution ofthe helium in the depth direction is positioned between the first localmaximum point and the second local maximum point, and the carrierconcentration at the first intermediate point is lower than the carrierconcentration at the second intermediate point.
 2. The semiconductordevice according to claim 1, wherein the carrier concentrationdistribution further has a third intermediate point positioned closestto the first local maximum point among (i) one or more lower-side localminimum points positioned between the first local maximum point and thelower surface and each having a local minimum value in the carrierconcentration or (ii) a plurality of lower-side flat points at which thecarrier concentration remains constant in the depth direction, theplurality of lower-side flat points positioned between the first localmaximum point and the lower surface, and the carrier concentration atthe first intermediate point is lower than the carrier concentration atthe third intermediate point.
 3. The semiconductor device according toclaim 1, wherein the carrier concentration at the first intermediatepoint is higher than a base doping concentration of the semiconductorsubstrate.
 4. The semiconductor device according to claim 1, wherein thecarrier concentration at the first intermediate point is lower than abase doping concentration of the semiconductor substrate.
 5. Thesemiconductor device according to claim 1, wherein the carrierconcentration distribution further has a third local maximum pointpositioned closest to the second local maximum point between the secondlocal maximum point and the upper surface among the one or moreupper-side local maximum points, and the second intermediate pointindicates the local minimum value in the carrier concentration betweenthe second local maximum point and the third local maximum point.
 6. Thesemiconductor device according to claim 2, wherein the carrierconcentration distribution further has a fourth local maximum pointpositioned closest to the first local maximum point among one or morelower-side local maximum points positioned between the first localmaximum point and the lower surface and each having a local maximumvalue in the carrier concentration, and the third intermediate pointindicates the local minimum value in the carrier concentration betweenthe first local maximum point and the fourth local maximum point.
 7. Thesemiconductor device according to claim 1, wherein a hydrogen chemicalconcentration distribution of the hydrogen containing region in thedepth direction has one or more hydrogen concentration trough portions,and in each of the one or more hydrogen concentration trough portions ahydrogen chemical concentration is equal to or higher than 1/10 of anoxygen chemical concentration, and in at least one of the one or morehydrogen concentration trough portions, the hydrogen chemicalconcentration is equal to or higher than a helium chemicalconcentration.
 8. The semiconductor device according to claim 7, whereinin each of the one or more hydrogen concentration trough portions, thehydrogen chemical concentration is equal to or higher than a carbonchemical concentration.
 9. The semiconductor device according to claim7, wherein the hydrogen chemical concentration distribution of thehydrogen containing region in the depth direction has one or morehydrogen concentration peaks, and at the one or more hydrogenconcentration peaks, the hydrogen chemical concentration is equal to orhigher than ½ of the oxygen chemical concentration.
 10. Thesemiconductor device according to claim 7, wherein in a hydrogenconcentration trough portion positioned deeper than the heliumconcentration peak among the one or more hydrogen concentration troughportions, the hydrogen chemical concentration is equal to or higher thanthe helium chemical concentration.
 11. The semiconductor deviceaccording to claim 9, wherein the one or more hydrogen concentrationpeaks include: a first hydrogen concentration peak; a second hydrogenconcentration peak positioned between the first hydrogen concentrationpeak and the upper surface and adjacent to the first hydrogenconcentration peak; a third hydrogen concentration peak positionedbetween the second hydrogen concentration peak and the upper surface;and a fourth hydrogen concentration peak positioned between the firsthydrogen concentration peak and the lower surface, and a full width athalf maximum of the helium concentration peak in the helium chemicalconcentration distribution is larger than an interval between twoadjacent hydrogen concentration peaks among the first hydrogenconcentration peak, the second hydrogen concentration peak, the thirdhydrogen concentration peak, and the fourth hydrogen concentration peak.12. The semiconductor device according to claim 11, wherein the firstlocal maximum point corresponds to the first hydrogen concentrationpeak, and the second local maximum point corresponds to the secondhydrogen concentration peak.
 13. The semiconductor device according toclaim 5, wherein a hydrogen chemical concentration distribution of thehydrogen containing region in the depth direction includes: a firsthydrogen concentration peak; a second hydrogen concentration peakpositioned between the first hydrogen concentration peak and the uppersurface and adjacent to the first hydrogen concentration peak; a thirdhydrogen concentration peak positioned between the second hydrogenconcentration peak and the upper surface; and a fourth hydrogenconcentration peak positioned between the first hydrogen concentrationpeak and the lower surface, and the third local maximum pointcorresponds to the third hydrogen concentration peak.
 14. Thesemiconductor device according to claim 13, wherein the second localmaximum point in the carrier concentration distribution is positioned(i) between the helium concentration peak and the upper surface in thedepth direction and (ii) at a depth position (a) same as a position ofthe second hydrogen concentration peak or (b) within 10% of a distancefrom the position of the second hydrogen concentration peak to the lowersurface, the third local maximum point in the carrier concentrationdistribution is positioned (i) between the helium concentration peak andthe upper surface in the depth direction and (ii) at a depth position(a) same as a position of the third hydrogen concentration peak or (b)within 10% of a distance from the position of the third hydrogenconcentration peak to the lower surface, and the carrier concentrationdistribution has no peak between the second local maximum point and thethird local maximum point.
 15. The semiconductor device according toclaim 6, wherein a hydrogen chemical concentration distribution of thehydrogen containing region in the depth direction includes: a firsthydrogen concentration peak; a second hydrogen concentration peakpositioned between the first hydrogen concentration peak and the uppersurface and adjacent to the first hydrogen concentration peak; a thirdhydrogen concentration peak positioned between the second hydrogenconcentration peak and the upper surface; and a fourth hydrogenconcentration peak positioned between the first hydrogen concentrationpeak and the lower surface, and the fourth local maximum pointcorresponds to the fourth hydrogen concentration peak.
 16. Thesemiconductor device according to claim 14, wherein the firstintermediate point is positioned at a depth position (i) same as aposition of the helium concentration peak or (ii) within 10% of adistance from the position of the helium concentration peak to the lowersurface.
 17. The semiconductor device according to claim 16, wherein avacancy defect concentration distribution of the hydrogen containingregion in the depth direction is distributed only between the firstlocal maximum point and the second local maximum point before and afterthe first intermediate point.
 18. The semiconductor device according toclaim 7, wherein in all of the one or more hydrogen concentration troughportions, the hydrogen chemical concentration is equal to or higher thanthe helium chemical concentration.
 19. The semiconductor deviceaccording to claim 1, further comprising a drift region provided betweenthe hydrogen containing region and the upper surface of thesemiconductor substrate, the drift region having a carrier concentrationlower than a carrier concentration of the hydrogen containing region.20. A fabrication method of a semiconductor device comprising asemiconductor substrate, the semiconductor substrate having an uppersurface and a lower surface, the fabrication method comprising: forminga hydrogen containing region by implanting hydrogen to the semiconductorsubstrate and performing first thermal treatment; implanting helium tothe semiconductor substrate such that at least a region of the hydrogencontaining region contains helium; and performing second thermaltreatment to the semiconductor substrate, wherein a carrierconcentration distribution of the hydrogen containing region in a depthdirection has: a first local maximum point having a local maximum valuein a carrier concentration; a second local maximum point positionedclosest to the first local maximum point among one or more upper-sidelocal maximum points positioned between the first local maximum pointand the upper surface and each having a local maximum value in thecarrier concentration; a first intermediate point positioned between thefirst local maximum point and the second local maximum point and havinga local minimum value in the carrier concentration; and a secondintermediate point positioned closest to the second local maximum pointamong (i) one or more upper-side local minimum points positioned betweenthe second local maximum point and the upper surface and each having alocal minimum value in the carrier concentration or (ii) a plurality ofupper-side flat points at which the carrier concentration remainsconstant in the depth direction, the plurality of upper-side flat pointspositioned between the second local maximum point and the upper surface,a highest point of a helium concentration peak in a helium chemicalconcentration distribution of the helium in the depth direction ispositioned between the first local maximum point and the second localmaximum point, and either one of implanting the helium to thesemiconductor substrate or performing the second thermal treatment tothe semiconductor substrate is conducted such that the carrierconcentration at the first intermediate point is lower than the carrierconcentration at the second intermediate point.
 21. The fabricationmethod according to claim 20, wherein the carrier concentrationdistribution further has a third intermediate point positioned closestto the first local maximum point among (i) one or more lower-side localminimum points positioned between the first local maximum point and thelower surface and each having a local minimum value in the carrierconcentration or (ii) a plurality of lower-side flat points at which thecarrier concentration remains constant in the depth direction, theplurality of lower-side flat points positioned between the first localmaximum point and the lower surface, and either one of implanting thehelium to the semiconductor substrate or performing the second thermaltreatment to the semiconductor substrate is conducted such that thecarrier concentration at the first intermediate point is lower than thecarrier concentration at the third intermediate point.
 22. Thefabrication method according to claim 20, wherein implanting thehydrogen to the semiconductor substrate is conducted such that ahydrogen chemical concentration distribution of the hydrogen containingregion in the depth direction has one or more hydrogen concentrationtrough portions, and in at least one of the one or more hydrogenconcentration trough portions, a hydrogen chemical concentration isequal to or higher than 1/10 of an oxygen chemical concentration, andimplanting the hydrogen to the semiconductor substrate is conducted suchthat in at least one of the one or more hydrogen concentration troughportions, the hydrogen chemical concentration is equal to or higher thana helium chemical concentration.